Download V. experimental setup of all-optical tunable delay

International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Measurement of Tunable All-optical Delay by
Using the Combination of Wavelength
Conversion and Fiber dispersion
Pyae Phyo Swe

Abstract— In this system, we report experimental
demonstration of an all-optical tunable delay element based on
the combination of wavelength conversion and fiber dispersion
with a total delay range of 3870ps. We present wavelength
conversion method that show with FWM of phase conjugation
property. Our delay technique has the combined advantages of
continuous control of a wide range of delays picoseconds to
nanoseconds and an output signal wavelength and bandwidth
that are the as that of the input. The bit error rate performance
of the delay element was characterized for a 10-Gb/s return to
zero RZ data channel. This result is enabled by conversing
wavelength that consists of 8 wavelengths dependent and a
continuously tunable stage. Two wavelength conversion stages
based on four-wave mixing were performed in order to achieve
wavelength –preserving operation. The wavelength optimized
optical phase conjugation scheme employed in the delay line in
capable of minimizing the residual dispersion for the entire
tuning range.
Index Terms— tunable optical delay, Four Wave Mixing
(FWM), Wavelength Conversion, Fiber Dispersion
I. INTRODUCTION
dependent delay of chromatic dispersion coupled with tunable
wavelength conversion to achieve relatively large tunable
delays.
In this method, tunable time-slot-interchange of 10- Gb/s
optical data packets using conversion-plus-dispersion-based
nearly 3800ps optical delay element is demonstrated. The
input signal is converted to different wavelengths using
four-wave-mixing (FWM) in highly-nonlinear-fiber (HNLF),
along with a reference signal containing the two extracted
signals. The two signals are retarded and advanced relative to
the reference signal using a dispersion module (SSMF).
Moreover, the conversion wavelength is converted back to the
original wavelength reusing four-wave-mixing (FWM)[5].
And, this signal will have dispersion .This dispersion is
eliminated with dispersion compensation module (SSMF)
.The performance of the proposed system is characterized
through
the
BER
curve
by
using
pseudo–random-bit-sequence (PRBS) and a BER= 10
achieved.
9
is
II. ALL-OPTICAL TUNABLE DELAY
Delay component that have the capability of buffering or
delaying information is required by communication networks.
In ultra high speed communications, information is encoded
in pulses; optical/electronic conversion of information is a
bottleneck for increasing the transmission rate. For
packet-switched networks, optical delays that are tunable over
reasonably long ranges and transparent to the packet
modulation format is needed by delaying and possibly
interchanging full data packets in the time domain .Thus ,it is
wanted to have all-optical components for buffering and
delaying signal pulses. Tunable optical delay components
also find application in optical coherence tomography [1],
optical control of phased array antennas for radio frequency
communication [2], and optical sampling, and pattern
correlation [3]. Tunable optical delays have been
demonstrated in the past using various methods ,including (1)
optical switching in combination with a discrete set of fixed
delays(2) slow-light-based photonic resonances[6] and
(3)chromatic dispersion based delay coupled with tunable
wavelength converters[7]. The techniques utilize wavelength
Manuscript received Apr 30, 2014.Pyae Phyo Swe, Department of
Electronic Engineering, Mandalay Technological University (e-mail:
[email protected]). Mandalay, Myanmar.
Various types of delay schemes using optical fibers have
been proposed based on chirped fiber Bragg gratings [2],
temporal gratings [4], wavelength conversion with dispersive
media [5], and slow light propagation[6].
In this system, tunable optical delay is implemented by
using the combination of wavelength conversion and fiber
dispersion. Wavelength conversion method is used by four
–wave mixing method (FWM). Fiber dispersion module used
with single mode fiber (SSMF).
Figure (1) Generics block diagram of tunable all optical delay by the
combination of wavelength conversion and fiber dispersion
Calculation of tunable optical delay;
Δt=
DLΔλ
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Tunable optical delay = converted wavelength
dispersion ×fiber length× tuning range of conversion
Shown in fig (1) is the generic block diagram of proposed
system. The input signal (t0) transmits in the wavelength
converter.It uses to convert was by using the method of
four-wave mixing (FWM) method.Optical fiber need to
change the signal.The signal (t1) can be converted in the
wavelength converter.After, this signal passes through the
dispersive element via single mode fiber (SMF). This applied
(t1) signal again flows in the wavelength converter to receive
original signal.This again used dispersion compensating
module (SMF) to eliminate dispersion due to the dispersive
element.Finally, the original signal (t1) with optical delay is
received.
needs the same phase of two signals. If the channels are
equally spaced, a number of the new waves will have the same
frequencies as the injected signals. The original signal waves
can strictly multi channel system performance. The efficiency
of four-wave mixing depends on fiber dispersion and the
channel spacing [3, 4]. The dispersion varies with
wavelength, the signal waves and the generated waves have
different group velocities. In FWM, if intensity is strong, new
waves will emit. Its main advantage is used in wavelength
conversion. This drawback has loss and lower conversion
range efficiency.
III. PRINCIPLE OF PROPOSED SYSTEM
Figure (3) operation of four -wave mixing with HNLF
Figure(2) Setup of all-optical tunable delay by the combination of
wavelength conversion and fiber dispersion; EDFA , erbium-doped fiber
amplifier ; HNLF ; highly nonlinear fiber ; Mod , modulator ; BER, bit error
rate; CW , continuous wave
Figure (2) shows setup the block diagram of all-optical
tunable delay. Firstly, the part of transmitter includes data
bits, laser and modulator. Modulator operates to transfer the
electrical signal to optical signal. In the part of optical delay
generation, component maintains the wavelength converter
and fiber dispersion module. Moreover, this part include
wavelength reconversion and dispersion compensator
module. Wavelength converter is used to convert the tuning
range of conversion. Fiber dispersion module used with single
mode fiber (SSMF). Wavelength reconverted to original
signal by using the wavelength reconversion method.
Dispersion compensation module reused the single mode
fiber (SSMF). The part receiver includes components to
measure the output signal.
IV. FOUR WAVE MIXING METHOD IN WAVELENGTH
CONVERSION
When wavelength channels are located near the
zero-dispersion point, three optical frequencies (vi, vj, vk)
will mix to produce a fourth inter modulation product vijk
given by
Vijk= vi+vj-vk with i,j ≠ k
A simple example has two waves at frequencies v1 and v2.
They mix and generate sidebands at 2v1-v2 and 2v2-v1. FWM
Figure (4) Illustration of FWM method
Figure (4) shows the FWM method. In this figure, we can
choose the desirable converted signal. If we choose the left
hand side of the converted signal1, this method can make the
signal degeneration. If not, we choose the right hand side of
the converted signal2; this method can use the phase
conjugation. In this system, we use the phase conjugation
method. So, this system used the dispersion compensating
module reuse single mode fiber (SSMF).
V. EXPERIMENTAL SETUP OF ALL-OPTICAL TUNABLE DELAY
The experimental setup is shown in fig (3).The RZ 10-Gb/s
data packet and the packet guard time of empty space is 7bits.
Packets are generated electronically and drive
Mach-Zehnder intensity modulators. We manually
programmed the pulse pattern generator (PPG) in order to
generate the stream of data packets, and the BERs were
measured by programming the PPG and error detector
accordingly. For RZ format, Gaussian pulse with 33% duty
cycle is used. The average input optical power to the first
transmission span is set to 0 dBm by EDFA and
EDFA-1.EDFA and EDFA-1 are used at 17 dB. The single
mode fiber (SMF1) has a positive dispersion of+ 698 ps/nm.
A 0.3-nm bandwidth at 1559.5 nm, and wavelength
2
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
converter-1 and wavelength converter-2 has wavelengths of
1559.5 nm and 1549.9 nm, respectively. Laser diode (LD)
λpump-1and LD λpump-2 is fixed at 1554.7nm and 1554.7
nm, respectively. LD λ pump-1and LD λ pump-2are tuned
according to the desired converted wavelength, λ c. The input
powers are: (i) for wavelength converter-1, λ1and
λpump-1are each 0 dBm, and (ii) for wavelength converter-2,
λ2 and λpump-2 are 0dBm and 0dBm. The converted
wavelength is -1.311 dBm for wavelength converter-1 and
-3.64 dBm for wavelength converter-2. The filters at the
output of wavelength converter-1 and wavelength converter
-2 have 3-dB bandwidths of each 0.4nm, respectively. The
receiver is a 10-Gbit/s p-i-n device.
Figure (7) show waveform of delay and dispersion at converted signal
1559.5nm
In this figure show the delay and dispersion at the
converted signal 1559.5nm.After pass through the SMF, the
output waveform have dispersion. This dispersion to
compensate used the dispersion compensation module. So,
after dispersion compensated have obtained the
approximately of original input signal. But this signal has
delay.
Figure (5) Tunable all-optical delay using opti system software
VI. PERFORMANCE OF PROPOSED SYSTEM
Figure (8) tunable all- optical delay versus
1553.9nm, 1556.3nm and 1559.5nm)
Figure (6) comparison of theoretical and experimental result of tunable
all-optical delay
conversion range (at
Figure (8) show the delay time versus conversion range. At
the converted signal 1553.9nm delay time range Δt is0ps.And
converted signal 1556.3nm delay time range, Δt have got
1640ps .At the converted signal 1559.5nm, delay time range
Δt=3870ps.In this signal, conversion range value is 4.8nm
and dispersion value is +17.45ps/nm km. Single mode fiber of
length is 40km.
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
(i)
Figure (9b) performance of the BER curve versus received power
In this fig (9b) show the performance of the BER curve
versus received power. After dispersion compensated, the
performance of the BER curve is better than the condition of
output signal without dispersion compensation.
VII. CONCLUSIONS
(ii)
This research focuses on design and implementation of
tunable all-optical delay by the combination of wavelength
conversion and fiber dispersion. Optical delay can have
change versus of the fiber length and pump wavelength. And
it is tuning the wide range of signal pulse .This research shows
tunable optical delay by using the OptiSystem software .So,
optical delay is important in optical system due to these above
factors. In this proposed method, system was used wavelength
converter and dispersive element to generate tunable optical
delay. Wavelength converter can be implemented by using the
four wave mixing method .This system can be converted
wavelength conversion range Δλ=5.6nm and dispersive
element uses single mode fiber, dispersion has +17.45ps/nm
km .In this experimental system, optical delay tuning range
can attain 3870ps.This system characterized the impact of the
system on performance by measuring the BER and power
penalty have 0.6dBm after dispersion compensated. Before
the dispersion compensation, power penalty have 1.6dBm.
(iii)
Figure (9a) comparison of eye diagram (i)at
back to back (ii)before
dispersion compensation (iii)after dispersion compensated
Figure (9a) indicate the comparison of eye diagram. At the
received power -23.3dBm,the peformance of fig (iii) is better
than the fig (ii).
ACKNOWLEDGMENT
The author would like to express sincere appreciation to
the Rector of Mandalay Technological University for kind
Permission to prepare for this journal. The author would also
like to give special thanks to my supervisor and all teachers in
EC Department and all who willingly helped the author
throughout the preparation of the paper. This paper is
dedicated to the author’s parents for continual and full support
on all requirements and moral encouragement.
REFERENCES
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time-delay scheme for feeding optically controlled phased-array
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
[3]
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Pyae Phyo Swe received her Bachelor of Technology (B.Tech) degree in
2006 and Bachelor of Engineering (B.E) degree in 2007 in Electronic
Engineering from Kyaukse Technological University, Myanmar. She is now
Master of Engineering (M.E) student in Mandalay Technological University,
Myanmar. Her research interests include optical fiber communications and
control system.
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